Hybrid scan antenna

ABSTRACT

A hybrid antenna system comprises two or more wave guide antenna sections which are physically separated and separately fed with radiant energy from a single source by dividing up energy from the source and feeding it into first ends of the various sections. Phase shifters are provided such that the radiant energy fed to successive sections is shifted in phase in such a manner that the overall radiated output beam from all of these sections constitutes a single beam which may be scanned in the same manner as though all of the sections were connected together to form a single elongated wave guide antenna. The provision of the antenna in sections makes it more convenient to locate the antennas on various portions of an aircraft to realize the same effect as an elongated single waveguide type antenna.

United States Patent [191 ill] 3,864,689

Young Feb. 4, 1975 HYBRID SCAN ANTENNA Primary Examiner-Eli Lieberman[76] Inventor. David Young, 627 N Attorney, Agent. or firm-Pastorrza &Kelly Beachwood Dr., Burbank, Calif. 91506 [57] ABSTRACT [22] Filed. Aug2, 1973 A hybrid antenna system comprises two or more wave guide antennasections which are physically separated [21] Appl. No.: 385,085 andseparately fed with radiant energy from a single source by dividing upenergy from the source and feeding it into first ends of the varioussections. Phase liil K585331113'iii/iii:3 iioifil i hhhhhhh hhhhhhh hhhhhhhh hhh hhhhhhh hhhhgh fed [58] Field of Search 343/l00 SA 768, 771,854, to successive sections is shifted m phase in such a manner that theoverall radiated output beam from all 343/705 of these sectionsconstitutes a single beam which may hhh resists:assesses?t en il12.15::UNITED STATES PATENTS 1 elongated wave guide antenna. The provision ofthe 2,777,122 V1957 Hcdcmll" 343/763 antenna in sections makes it moreconvenient to lo- 3936310 5/l962 Lchim F 343/854 cate the antennas onvarious portions of an aircraft to 3,041,605 6/l962 GOOdWlI'l 8121i.343/854 realize the same effect as an elongated Single wave guide typeantenna.

3 Claims, 4 Drawing Figures I2 ll Synch I r F Motor I Microwave 355dPh'use "put T COupler l Shifter PEJENTEU FEB 4 I975 SHEEi 2 [IF 2 PhaseDet.

Synch Phase I Motor Shifter i i l I Microwave 3 D [3 (It) (-9-) lnput 7Hybrid Phase Phase 3O Coupler Shifter Shifter J l 3i 33 i 39 B IElectro- 40 [4| L Mechanical Transducer 43 Position Sensor Synch MotorPhase 48 I 54\ Detector 7 5l- Microwave Digiffll m Hybrid phpse 46Coupler Shifter HYBRID SCAN ANTENNA This invention relates generally tomicro-wave antennas and more particularly to wave guide scanning typeantennas used in self-contained aircraft radar systems.

BACKGROUND OF THE INVENTION In my co-pending patent application Ser. No.353,201 filed Apr. 20, 1973, now U.S. Pat. No. 3,829,862 and entitledRIDGE SCAN ANTENNA, there is shown and described an elongated waveguideantenna which incorporates an electro-mechanical scanning means toprovide for a fan-shaped radiated beam in'a vertical plane which may bescanned back and forth in azimuth. In another of my co-pending patentapplication Ser. No. 353,129, also filed Apr. 20, 1973 and entitledCONTINUOUS SCANNING WAVE GUIDE ANTENNA, now U.S. Pat. No. 3,803,620issued Apr. 9, 1974 there is described an antenna system which willgenerate the same type of beam but wherein a continuouselectro-mechanical scanning arrangement is provided.

In both of the above co-pending patent applications, the antennasinvolved are in the form of elongated wave guides which may have adimension for example of feet in length. The length of the overallwaveguide type of antenna is important in obtaining the necessary narrowvertical beam width. The antennas themselves are most advantageouslyused in perspective radar systems incorporated in an aircraft. In thisrespect, reference is had to my co-pending application Ser. No. 847,121filed Aug. 4, 1969 and entitled AIR- CRAFT CONTAINED PERSPECTIVERADAR/DIS- PLAY AND GUIDANCE FOR APPROACH AND LANDING, now U.S. Pat. No.3,778,821, issued Dec. 11, 1973.

Because the waveguide scanning type antennas are of long physicaldimensions, there can be a serious problem in finding an acceptablelocation for the wave guide antenna in the aircraft. The problem is nottoo critical in the case of fairly large aircraft, the leading edge ofthe wing serving as a satisfactory location for accommodating thewaveguide antenna. In fact, for fairly large aircraft, the wing flapitself constitutes an excellent location for such an antenna all as setforth and described in my further co-pending patent application Ser. No.355,065 filed Apr. 27, 1973, and entitled FLAP ANTENNA.

However, for smaller aircraft and even in some larger types of aircraft,it is desirable to locate any antennas in suitable radomes rather thanin the leading edge of wings or in other areas. 'In the case of a 10foot long X- band antenna suitable for a perspective radar, thecommercial jet radome would not be capable of accommodating thenecessary structure. By using a higher frequency, for example, theKa-band a 3 foot length wave guide antenna would operate to provide therequired narrow beam width since it is equivalent in length to a 10 footantenna operating at X-band frequency and thus could be accomodated inthe radome. Of course if a Ka-band wave guide antenna of a 10 footlength or an X-band of 30 foot length could be constructed andaccommodated on an aircraft, an extremely narrow beam could be generatedin a vertical plane which would be very useful.

Aside from the foregoing problems of physical location of a long waveguide antenna, there are also the very serious mechanical problemsinvolved in effecting a proper scanning in a long wave guide type ofstructure. For example in the ridge scan antenna as described in myheretofore referred to patent application of the same title, a ridgemember is caused to reciprocate back and forth into a side opening ofthe waveguide antenna over its entire length to effect a shift in thephase velocity of radiation within the guide and thereby cause thedesired scanning in azimuth to take place. It is vitally important thatthe ridge member move absolutely parallel to itself in entering andleaving the wave guide and in the case of very long wave guides forexample, over wave lengths such as 10 feet for X-band or 3 feet forKa-band, it can become a serious problem in tolerances to provide such amechanical system for accurately moving the ridge member.

Thus from both the standpoint of physical location and the standpoint ofmechanical tolerances in effecting a scanning operation, it is mucheasier to work with shorter length antennas. On the other hand, and asnoted, the shorter length antennas are not capable of providing thedesired narrow beam width of the resultant radiant energy beam in avertical plane.

BRIEF DESCRIPTION OF THE PRESENT INVENTION The present inventioncontemplates a novel hybrid scan antenna system wherein at least two andpreferably several physically separated elongated waveguide antennasections are provided together with coupler means for receivingelectro-magnetic energy from the single main source and dividing it tofeed equal amounts to first ends of the antenna sections. Means are alsoprovided for scanning in synchronism the radiant energy emitted by eachof the physical separate antennas. This scanning means may take the formof ridge scanners for each particular section or continuous typesscanning systems for each individual section such as described for theheretofore provided long single wave guide antenna as described in myreferred to copending applications. However, because the individualsections are each substantially shorter than the over-all length of asingle continuous antenna which would result if all of the sections wereconnected end to end, great accuracy can be realized in the scanning ofthe individual sections. Suitable means are provided to assure that thescanning of the individual sections is in synchronism.

In addition to the foregoing, the invention provides a phase shift meansexterior of the antenna sections including means positioned to receivethe energy fed to one of the sections and shift its phase relative tothe energy fed to the other or preceeding section, there being providedmore than one phase shifter if there are more than two sectionsinvolved. The degree of phase shifting in turn is controlled by acontrol means connected to the phase shift means and responsive to thescanned position of radiant energy emitted by the antennas to shift thephase of the energy fed to the one antenna and in the case of aplurality of sections successively shift the energy to the subsequentsections all in such a manner that the radiant energy from all of thesections is in the form ofa single beam which is scanned the same asthough the sections were connected end to end to form a single longcontinuous wave guide antenna.

By adjusting the degree of phase shifting and synchronizing the phaseshifting with the electromechanical scanning arrangement, the individualantenna sections can be located at various different physical portionsof the aircraft and the requirement of a space on the aircraft toaccommodate a single long wave guide type antenna is avoided.

BRIEF DESCRIPTION OF THE DRAWING A better understanding of the inventionwill be had by now referring to the accompanying drawings in which:

FIG. I is a perspective view of an aircraft incorporating the hybridantenna of the present invention for generating a fan-shaped radar beamcapable of sweeping in azimuth;

FIG. 2 is a schematic block diagram illustrating the manner in which asingle radiant energy fan-shaped beam as shown in FIG. 1 can be obtainedfrom two physically separate wave guide antenna sections in accord witha first embodiment of the invention;

FIG. 3 is a block diagram similar to FIG. 2 but showing an additionalfeed-back system for maintaining phase shift accuracy in the system; and

FIG. 4 illustrates a third simplified embodiment wherein a digital typephase shifter is used.

Referring first to FIG. 1, there is shown an aircraft l equipped withhybrid antenna sections l1, 12, 13, 14, and in accord with the presentinvention. The physical location of these sections, one of which isshown in the nose portion of the aircraft and the remaining on leadingedge portions of the wings is arranged to provide for a singlefan-shaped radiant energy beam 16 which may be swept in azimuth asindicated by the double headed arrow the same as though the individualsections were all connected end to end to provide a single elongatedcontinuous wave guide antenna.

It will be evident from FIG. 1 that if the antenna sections wereconnected together as described, there would be no convenient physicallocation on the air- I craft to accommodate such a long antenna.However,

by providing the antenna in hybrid sections as shown, the sectionsthemselves can be properly accommodated.

Referring now to FIG. 2 there is shown a first system for assuring thatthe individual hybrid antenna sections function in such a manner as toprovide for an overall single radiated beam of narrow beam width. InFIG. 2, the antenna sections 11 and 12 described in FIG. 1 are shown theseparation spacing being greatly exaggerated. In this respect, there isno problem in locating one of the sections ahead or behind the other aslong as their longitudinally separated distance is not great. Forexample, the antenna sections 12 and 13 of FIG. 1 are translationallydisplaced so that the antenna section 13 is ahead of the antenna section12. However, if the antenna section 13 were moved back to a projectedposition in alignment or close to alignment with the antenna section 12,its physical separation at the adjacent ends would be small and it isimportant that this distance be kept small.

As shown in FIG. 2, there is provided a first synchronous motor 17 fordriving a suitable scanning element in the antenna section 12. A secondsynchronous motor 18 in turn drives the corresponding scanning elementin the antenna section 11 and is maintained in exact synchronism withthe synchronous motor 17 as by the resolver 19.

If a ridge type scan member is employed such as described in myheretofore referred to co-pending patent application, it will beappreciated that control of the ridge for the shorter length sections 11and 12 can more readily be carried out and with greater accuracy than ispossible for a single ridge in a wave guide of twice the length ofeither of the individual sections.

Referring to the lower portion of FIG. 2, there is shown a micro-waveinput line 20 which would be a feeding wave guide from a single sourceof electromagnetic energy. This input passes through a hybrid couplermeans 21 which simply functions to divide the energy and feed it inequal amounts to first ends of the antenna sections as indicated by thelines 22 and 23. A phase shift means in the form ofa phase shifter 24exterior of the antenna sections is positioned to receive energy fromthe line 23 and shift its phase relative to the energy in line 22 fed tothe other of the said sections.

The system is completed by control means in the form of the connection25 from the synchronous motor 18 to the phase shifter 24 which functionsto supply a signal to the phase shifter in response to the scan positionof the radiant energy emitted by the antennas. This scanned position isa function of the position of the ridge member in the event ridgescanning is employed which in turn is determined by the position of thesynchronous motor at any instance in time. The signal to the phaseshifter 24 from the line 25 shifts the phase of the energy fed to theantenna 11 in such a manner that the radiant energy from the sections 10and 11 is in the form of a single beam which scans the same as thoughthe sections were connected end to end to form a single long continuouswave guide antenna.

The result of the phase shifting can be best understood by referring tothe wave fronts of the radiated energy in FIG. 2 wherein the portion 26of the wave front would represent energy from the antenna section 12 andthe dashed portion 27 would represent energy from the section 11 at agiven scan position. Essentially, the action of the phase shifter 24shifts the energy wave front 27 to the position 27' in exact alignmentwith the wave front 26 so that there results the single radiant energybeam as described.

The amount of phase shift is different for each scan position. Forexample, when the radiated beam is directed forwardly along a lineperpendicular to the longitudinal axis of the antenna sections; that is,broadside, no phase shift between the energy at the input lines 22 and23 to the sections respectively, takes place. As the beam scans pastbroadside, then the phase shifter 24 acts to shift the phase of theenergy fed to the one antenna section 11 in a continuous manner such asto bring about the condition of a simulated single beam as describedwith respect to the scanned position illustrated in FIG. 2.

It will be understood that the FIG. 2 relates to only two antennasections and that in actuality, several sections may be provided toprovide the equivalent wave front of a single elongated antenna oflength equal to the sum of the total number of sections. Further phaseshifters corresponding to the phase shifter 24 would be provided for thesubsequent antenna sections so that the final overall radiated beamwould have a flat wave front corresponding to the line 26 and 27' ofFIG. 2.

A further advantage of the hybrid scanner described in FIG. 2 inaddition to the advantage of spaced location and better tolerances inthe mechanical scanning is the fact that less energy is lost in theoverall hybrid antenna system. For example, considering an X-bandantenna feet long there is a three decibel power loss. If two 10 footantennas are combined as illustrated in FIG. 2, the total loss wouldstill only be three decibels while the loss of an equivalent straight 20foot antenna would be 6 decibels. Thus the two antenna sections functiontwice as efficiently as an equivalent single long antenna. Clearlygreater efficiency will be achieved for a larger number of sections.

Another advantage of providing antenna sections rather than a singleelongated antenna is that each section is less sensitive to aircraftchanges in structure due to variations in wing loading by way ofexample. In other words, variations in the wing loading would be lesslikely to affect the synchronous motor driving of the individualsections as opposed to driving a single long antenna.

FIG. 3 illustrates a system similar to FIG. 2 but wherein a feedbackmechanism has been provided to maintain absolute accuracy in the phaseshifting of the energy fed to one antenna relative to the energy fed tothe other.

As shown, there are provided antenna sections 11 and 12 wherein therecorresponding electromechanical scanning mechanisms which might take theform of individual ridges are driven in synchronism by a synchronousmotor 28. In the showing of FIG. 3, the ridge for the one antenna 11 isindicated as being driven by the synchronous motor 28 by the dash line29. It will be understood that a separate synchronous motor could beutilized and it should also be understood that the section 11 need notbe in alignment with section 12 but could still be driven by the samesynchronous motor through suitable displacing gears.

As in the case of FIG. 2, there is provided a microwave input line 30passing to a coupler 31 dividing the radiant energy into equal amountsfor feeding along lines 32 and 33 to first ends of the antennas l2 and11 respectively. However, the energy in the line 33 first passes througha plus-minus feedback controlled phase shifter 34 and thence to a plusphase shifter 35 prior to being fed into the one antenna 11. The energyat the other end of the one antenna 11 passes into a minus phase shifter36 and thence to one side of a feedback phase detector 37. The otherside of the phase detector 37 receives energy from the other end of theother antenna 12 as indicated by the line 38 to provide for an errorsignal on an output line 39 passing to the plusminus feedback controlledphase shifter 34.

The phase shifter 35 is controlled by an input signal line 40 and thephase shifter 36 is simultaneously controlled by the same signal on aline 41. It will be understood that the minus phase shifter 36 shiftsthe phase in an exactly opposite direction to the plus phase shift bythe phase shifter 35. The controlled signals on line 40 and 41 arederived from an electro-mechanical transducer position sensor 42responsive to the position of the scanning means as indicated by thedashed line 43.

In the operation of the circuit of FIG. 3, the phase shifter 35 shiftsthe phase of the energy fed to the antenna section 11 in such a mannerthat the wave front radiated therefrom is in proper flat relationship oralignment with the wave front radiated from the antenna section 12. Theproper alignment is maintained for the various scanner positions inazimuth by continuously shifting the phase of the phase shifter 35through the electro-mechanical transducer position sensor 42 and signalline 40 all as is accomplished by the corresponding elements asdescribed in FIG. 2. However, in FIG. 3 the minus phase shifter 36receives the energy from the other end of the antenna section 11 andshifts its phase in a manner precisely opposite to the phase shifter 35so that the input to one side of the phase detector 37 is in phase withthe energy fed on line 33 passing through the plus-minus phase shifter34 to the phase shifter 35. As stated, the energy from the other end ofthe antenna section 12 passes in line 38 to the phase detector 37 andthis energy should be directly in phase with the energy passed to thefirst side since the phase shift accomplished by the phase shifter 35has been canceled out be the phase shifter 36. However, should there beany mechanical differences or discrepancies in the synchronizing of themechanical scanning of the two antenna sections resulting in a slightphase shifting, the phase detector 37 will detect any such slightdifference in phases of the energy fed to the respective sections andprovide an error signal on the line 39 which passes to the plus-minusfeedback controlled phase shifter 34. This phase shifter will effect aslight shift in the phase of the energy on line 33 to phase shifter 35in a proper direction to null any error signal from the phase detector37 so that the desired proper phase relationship is maintainednotwithstanding the presence of slight mechanical differences in themechanical scanning operations of the sections.

Referring now to FIG. 4 there is shown a simplified embodiment of theinvention wherein rather than continuously varying the phasewith thescanning of one section relative to another, a digital type phaseshifter is utilized.

Referring in detail to FIG. 4 the antenna sections 11 and 12 are scannedsynchronously as by a synchronous motor 44 and suitable couplingconnection 45. A micro-wave input line 46 passes through a coupling 47to divide energy along lines 48 and 49 to first ends of the antennas l2and 11 respectively.

The digital phase shifter is characterized in that it will shift thephase of an incoming signal in a discreet step rather than in acontinuous manner in response to an input signal. For example, it mighteffect a phase shift whenever it receives such an input signal.

Control of the digital phase shifter 50 is accomplished by passingenergy on lines 51 and 52 into the two sides of a phase detector 53, theoutput line 54 of which provides an input signal to the digital phaseshifter 50. The phase detector 53 is arranged to provide such an inputsignal only when the energy on the lines 51 and 52 is out of phase by apredetermined amount.

In considering the operation of the circuit of FIG. 4, it will beunderstood that in the absence of any phase shifter 50, the resultantbeam from the radiation from each of the antenna sections 11 and 12would alternately peak and null as scanning took place. For example,when scanning is directly broadside and no phase shift is requiredbetween the energy supplied on lines 48 and 49, the wave front of theenergy radiated would be flat and in a peak condition. However, when theangle of scan to either side of broadside assumes certain values oneradiation would cancel the other and there would result a null. Forexample, if the two wave guide sections were each 10 feet long and atX-band each would have its own approximate 0.8 beam width and incombination the beam width would be 0.4. However, the 0.4 beam whilescanning would null out about every 0.8. This result would not seem tobe a very useful antenna but in reality, the nulls are very narrow andin the presence of strong signals the nulls would not be very prominenton a practical radar display. In essence, then, the hybrid antenna inits most simplified version might function to some extent without anyphase shift.

In the circuit of FIG. 4, however, a compromise phase shift system isprovided which will fill in the nulls and peaks of the resultant outputbeam. While this system is not as satisfactory as that described inconjunction with FIGS. 2 and 3 wherein automatic continous phaseshifting takes place so that the beam is always peaked, it is far moreeconomical and may be sufficiently practical for practical applications.

Considering the actual manner in which the filling in t e ll P l .t spase tQLSS is s to provide anTnput signal on the line 54 whenever thephase of the input energies supplied by leads 51 and 52 approaches apredetermined difference; for example, when the two input energiesapproach 180 out of phase. Generation of the input signal on the line 54will then digitally shift the phase shifter 50 and if this phase shifteris set for shifting phase in 180 steps, the phase on the line 51 will beshifted 180 and thus will be appreaching a condition in phase with theenergy on line 52. Thus a condition wherein there would normally be anull is filled in by the sudden reversal of the phase on the line 51 dueto actuation of the digital type phase shifter. The wave front of theresultant output beam as far as peaks and nulls are concerned wouldappear scalloped. By providing digital stepping of the phase shifter50in shorter steps; for example, 90 or even 45,

the number of scallopes would increase and would all be shallower andclearly as the number of digital phase shifts steps were made stillshorter, the operation would approach that of the FIG. 2 embodiment.

From the foregoing description, it will be evident that the presentinvention has provided unique hybrid antenna systems wherein theadvantages of a long antenna, tolerances in mechanical scanning, andefficient use of power are all realized.

In essence, the present invention combines the most advantageousfeatures of a completely electronic scanning antenna and a completelymechanical scanning antenna. The use of total electronic scanningantenna systems is much too complex and expensive for many current andfuture applications but the present invention takes advantage of thesmall, rapid electronic phase shifter design used only a few times andcombines it with the mechanical or ridge scanner type of antenna, thusutilizing the best of both techniques.

Moreover, each of the hybrid sections are the same and thus can beeconomically manufactured. In any particular application, any number ofsections to make up an overall antenna may be selected depending uponthe economics, size of the aircraft, and beam width desired.

What is claimed is:

l. A hybrid scan antenna comprising, in combination:

a. at least two physically separated elongated wave guide antennasections;

b. coupler means for receiving electromagnetic energy from a singlesource and dividing it to feed equal amounts to said antenna sections;

c. mechanical means for scanning radiant energy emitted by each of saidantennas, said scanning being sychronized;

d. phase shift means exterior of the antenna sections including meanspositioned to receive the energy fed to one of said sections and shiftits phase relative to the energy fed to the other of said sections; and,

e. control means connected to said phase shift means and responsive tothe scanned position of radiant energy emitted by the antennas to causethe phase shift means to shift the phase of the energy fed to said oneantenna in a manner such that said radiant energy is in the form of asingle beam which is scanned the same as though the sections wereconnected end to end to form a single long continuous wave guideantenna, said phase shift means shifting the phase of energy receivedthereby in a continuous manner as a linear function of a varying inputsignal, said control means including means for deriving said varyinginput signal for the phase shift means from said mechanical means forscanning radiant energy.

2. An antenna according to claim 1, in which said phase shift meansincludes a plus-minus feedback controlled phase shifter, a plus phaseshifter, a minus phase shifter, and a feedback phase detector, saidplus-minus feedback controlled phase shifter receiving radiant energyfed to one of said sections and passing it through said plus phaseshifter, the output from said plus shifter passing to the first end ofsaid one antenna section, said minus phase shifter receiving energy fromthe other end of said one section and shifting its phase in a manneropposite to the phase shift by said plus phase shifter to provide energyto one side of said feedback phase detector so that said energy is inphase with the phase of the energy supplied from said plus-minusfeedback controlled phase shifter, radiant energy from the other end ofthe other of said antenna sections passing to the other side of saidfeedback phase detector, said feedback phase detector providing anoutput error signal proportional to any phase difference of the energyreceived in its sides to said plus-minus feedback controlled phaseshifter to effect a correction in the phase of the energy passed to saidplus phase shifter in a manner to reduce the error signal towards zero,said control means connecting to both said plus and minus phase shiftersto simultaneously control the phase shifts thereof which take place inopposite directions, in accordance with the scan position of the radiantenergy emitted by the antennas.

3. An antenna according to claim 1, in which said phase shift meanscomprises a digital type phase shifter for shifting the phase of energyfed thereto in discrete steps in response to an input signal, saidcontrol means comprising a phase detector having its sides connected toreceive radiant energy fed to said first ends and providing said inputsignal to said phase shifter whenever the difference in phase of saidenergy reaches a predetermined amount.

1. A hybrid scan antenna comprising, in combination: a. at least twophysically separated elongated wave guide antenna sections; b. couplermeans for receiving electromagnetic energy from a single source anddividing it to feed equal amounts to said antenna sections; c.mechanical means for scanning radiant energy emitted by each of saidantennas, said scanning being sychronized; d. phase shift means exteriorof the antenna sections including means positioned to receive the energyfed to one of said sections and shift its phase relative to the energyfed to the other of said sections; and, e. control means connected tosaid phase shift means and responsive to the scanned position of radiantenergy emitted by the antennas to cause the phase shift means to shiftthe phase of the energy fed to said one antenna in a manner such thatsaid radiant energy is in the form of a single beam which is scanned thesame as though the sections were connected end to end to form a singlelong continuous wave guide antenna, said phase shift means shifting thephase of energy received thereby in a continuous manner as a linearfunction of a varying input signal, said control means including meansfor deriving said varying input signal for the phase shift means fromsaid mechanical means for scanning radiant energy.
 2. An antennaaccording to claim 1, in which said phase shift means includes aplus-minus feedback controlled phase shifter, a plus phase shifter, aminus phase shifter, and a feedback phase detector, said plus-minusfeedback controlled phase shifter receiving radiant energy fed to one ofsaid sections and passing it through said plus phase shifter, the outputfrom said plus shifter passing to the first end of said one antennasection, said minus phase shifter receiving energy from the other end ofsaid one section and shifting its phase in a manner opposite to thephase shift by said plus phase shifter to provide energy to one side ofsaid feedback phase detector so that said energy is in phase with thephase of the energy supplied from said plus-minus feedback controlledphase shifter, radiant energy from the other end of the other of saidantenna sections passing to the other side of said feedback phasedetector, said feedback phase detector providing an output error signalproportional to any phase difference of the energy received in its sidesto said plus-minus feedback controlled phase shifter to effect acorrection in the phase of the energy passed to said plus phase shifterin a manner to reduce the error signal towards zero, said control meansconnecting to both said plus and minus phase shifters to simultaneouslycontrol the phase shifts thereof which take place in oppositedirections, in accordance with the scan position of the radiant energyemitted by the antEnnas.
 3. An antenna according to claim 1, in whichsaid phase shift means comprises a digital type phase shifter forshifting the phase of energy fed thereto in discrete steps in responseto an input signal, said control means comprising a phase detectorhaving its sides connected to receive radiant energy fed to said firstends and providing said input signal to said phase shifter whenever thedifference in phase of said energy reaches a predetermined amount.